Conductive urethane roller

ABSTRACT

An electrically conductive or semi-conductive polymeric material including a metal salt dissolved in a polymer. The metal salt is complexed with the polymer, which is what provides the material with its conductive properties. The materials have a resistivity of between 10 5  and 10 12  ohms-cm.

FIELD OF THE INVENTION

[0001] This invention relates to the field of polymers, particularlyurethane rubbers and foams, and to a method of making such polymerselectrically conductive or electrically semi-conductive.

BACKGROUND OF THE INVENTION

[0002] In the prior art, polymers, particularly urethane rubber, havebeen used for a variety of applications in which it is desirable thatthe product have some electrical conductivity, either throughout theproduct itself or at least on the exposed surface of the product.

[0003] One example involves rollers used in many printers to helptransport paper or carry toner in electrograhic printing. The rollersare often made of a polymer such as polyurethane or covered with asimilar polymer to facilitate their paper-carrying or toner transferability. Different materials, including rubber, may be used in place ofpolymers for these applications, but because these polymers are muchmore durable than rubber, they are preferred. Most polymers do notconduct electricity, however, and static charges, which adversely effectthe operation of the printer, can build up on the rollers. A similarproblem exists if rollers of the same material are used for otherpurposes, such as carrying semiconductors as part of a semiconductormanufacturing process. Other end uses require conductive orsemi-conductive parts as well.

[0004] As a result, there have been attempts make such polymer partselectrically conductive. In some cases, the part made from the polymerhas been coated with an electrically conductive material. Unfortunately,these coatings have short life spans, and some are toxic. Anotherapproach has been to disperse an electrically-conductive material in thepolymer when the part is being fabricated. These electrically-conductivematerials have included metal powders such as silver, copper, andnickel, and also materials such as carbon black, graphite, or otherconductive polymers. However, the resulting products have severalserious drawbacks. In the prior art, in order to make the polymer evensemi-conductive, a large amount of conductive filler, e.g., metal powderlike carbon black, had to be used, often as high as 10% to 40% of theoverall mixture by weight. This degraded the mechanical and thermalproperties of the resulting polymer part. Moreover, because of the size,and nature of the conductive particles, as well as the way in which theparticles were mixed with the polymer, conductivity was not very great.

[0005] Another related problem is that it is very difficult, due to therelative size and weight of the added particles and the difficulty indispersing them into the polymeric composition, to achieve a uniformdistribution of the conductive material throughout the polymer. As aresult of an uneven distribution, the electrical conductivity of theresulting product is not uniform, and the resulting product's mechanicaland thermal properties suffer as well. As a result of all this, ingeneral, products made from such compounds have been far less thansatisfactory, and in fact, in some applications, become high maintenanceitems.

[0006] Finally, a related problem is that it is often desirable toselect the specific conductivity of an polymer in advance, as differentend applications preferentially require parts with differentconductivities. Selection was not really possible with the prior artmethods of making semi-conductive polymers.

[0007] Accordingly, one object of the invention is to provide a methodby which polymeric materials may be made electrically conductive,without the need for conductive coatings or large amounts of conductivefillers.

[0008] Another object of the invention is to provide a method of makingan electrically conductive polymeric material so that the resultingproduct has uniform electrical conductivity throughout.

[0009] Another object of the invention is to provide a method of makingan electrically conductive polymeric material so that the relativeelectrical resistance of the resulting product may be varied with a highdegree of accuracy.

[0010] Another object of the invention is to provide a method of makingan electrically-conductive polymeric material whereby the mechanical andthermal properties of the resulting product are not degraded from whatwould be expected with a similar material which was non-conductive.

[0011] Another object of the invention is to provide a polymericmaterial which is electrically conductive and which may be molded andmachined.

[0012] Another object of the invention is to provide anelectrically-conductive polymeric material that is free of voids.

[0013] Another object of the invention is to provide anelectrically-conductive polymeric material that when used on the surfaceof rollers, e.g., in a printer, inhibits build-up a static charge on theroller.

[0014] Another object of the invention is to provide a polymericmaterial with good thermal stability.

SUMMARY OF THE INVENTION

[0015] The invention features an electrically conductive orsemi-conductive polymeric material that has a resistivity of between 10¹² ohm-cm and 10 ⁵ ohm-cm. The material is a solid solution of metalsalt dissolved in a polymer. The metal salt is complexed with thepolymer, which is what provides the material with its conductiveproperties. Depending on the desired resistivity, the quantity of metalsalt in the material can be varied, although preferably the materialincludes only a small amount (less than 1%, more preferably less than0.1%) of the metal salt by weight. Because only a small amount of themetal salt is included in the material, the material has good mechanicaland thermal properties. These properties, coupled with the conductivenature of the material, make the material suitable for use as coatingson, e.g., rollers used on paper printers.

[0016] The preferred polymers contain, e.g., nitrogen, oxygen, sulfur orhalide atoms, or unsaturated (double and triple bond) groups, which areavailable for complexing with the metal salt. Preferred polymers includeelastomeric polymers like polyurethanes and rubbers, adhesive polymers,and plastics. When rubbers are used, the material also preferablyincludes a plasticizer.

[0017] Preferred metal salts suitable for use in the material includetransition metal halides like CuCl₂, CuBr₂, CoCl₂, ZnCl₂, NiCl₂, FeCl₂,FeBr₂, FeBr₃, CuI₂, FeCl₃, FeI₃, and FeI₂. Other preferred salts includeCu(NO₃)₂, copper lactate, copper tartrate, iron phosphate, iron oxalate,LiBF₄, and H₄Fe(CN)₆.

[0018] The invention also features a method of preparing these polymericmaterials. Generally, the method includes making a homogenous solutionof the metal salt in a polymer or polymer precursor, and curing thecomposition. When the polymer precursor is an isocyanate functionalprepolymer, the solution also includes an extender (polyol or polyamine)that reacts with the isocyanate groups during curing to form apolyurethane resin. This method results in an even distribution of themetal salt throughout the polymeric material, which provides thematerial with uniform conductivity throughout.

[0019] The conductive elastomers are suitable for use in a variety ofindustrial applications to control surface charge and to provide goodheat conductivity and expanded life. For example, the polymers can beused to coat the belts, shafts, wheels, inserters, and paper handlingand copier toner pick-up rollers in paper printers. The polymer can beused to coat car bodies, print circuits, seals, and to dissipate chargesin various other electrical applications, such as coating on belts thatare used to transport semiconductor wafers during manufacture. Theconductive plastic materials (such as nylon) can be used to coat discdrives, machine body parts, cabinets, and carry cases.

[0020] Other features and advantages of the invention will be apparentfrom the description of the preferred embodiment thereof, and from theclaims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The preferred polymers are polyurethanes. The preferred method ofpreparing conductive polymeric materials including a polyurethane is tomix an extender (polyol or amine) or an isocyanate-functional prepolymerwith a solution of a metal salt. The mixture is then cured. Of course,other standard ingredients, like a cure accelerator or a flameretardant, may be included in the mixture.

EXAMPLE 1 Conductive Laser Roller

[0022] A steel core was coated with an adhesive (Thixon AP 3437 fromMorton International, West Alexandria, Ohio). The part was thencompletely dried.

[0023] A 5% solution of copper chloride was prepared as follows. In aone liter container, 475 grams of Pyrol PCF (tri(B-chloropropyl)phosphate, available from Akzo Chemical Inc., Chicago, Ill.), 475 gramsof Fyrol CEF (tri(B-chlorethyl) phosphate, available from Akzo ChemicalInc., Chicago, Ill.), 50 grams of dried copper chloride (available fromAldrich Chemical Company, Milwaukee, Wis.), and 6 grams of PluracolTP-440 (polyol available from BASF Corporation, Parsippany, N.J.) weremixed under mechanical stirring at 200-500 rpm and at 220 F for 2 hours.A green solution was obtained.

[0024] A 55 gallon resin tank (made by Amplan Inc., Middlesex, N.J.,equipped with vacuum, stirring, pressure, venting valves and temperaturecontrol) was filled with a polyisocyanate functional prepolymer,Vibrathane 8011 (available from Uniroyal Chemicals, Middlebury, Conn.)and the temperature raised to, and maintained at, 170° F. In a 15 litercontainer, 8200 grams of Isonol 93 (available from the Upjohn Co.,Kalamozoo, Mich.), 1400 grams of TIPA (tributoxyethyl phosphate,available from FMC Corp. of Nitro, W.Va.), 160 grams of copper chloridesolution (5%) and 48 grams of Metacure T-12 (dibutylton dilaurate,available from Air Products, Allertown, Pa.) were mixed with mechanicalstirring at 200-500 rpm for 5 minutes at room temperature. The TIPAincreases the solubility of the ingredients; the T-12 is a catalyst. Themixture was then degassed for 30 minutes under vacuum. The mixture wastransferred to the 5 gallon curative tank (made by Amplan Inc. andequipped with a mechanical mixer).

[0025] Both the prepolymer and the curative were mixed through anAutomatic Process Control dispenser to produce a uniform mixing. Byadjusting the flow rate for each tank, 148600 grams of the prepolymer(Vibrathane 8011) and 9800 grams of the curative were mixed thoroughly.

[0026] The mixture was charged to each casting mold surrounding thesteel cores. The mixture then was cured in the casting mold at 260° F.for 20 minutes. It was then demolded and left in the oven at 230° F. for12 hours.

[0027] The cased roller was then ground to obtain the specifieddimensions. The finished part has hardness of 53 Shore A and hadelectrical resistivity of 3×10⁹ ohms-cm.

EXAMPLE 2 Conductive Laser Roller

[0028] A second conductive laser roller was made by an analagousprocedure as in Example 1, except that the formulation was changed tothe following: Components Weight (grams) 8011 148600  I-93 8200 TIPA1400 Copper Chloride  800 T-12   6

[0029] The finished part had a hardness of 53 Shore A and a resistivityof 1.5×10⁹ ohms-cm.

EXAMPLE 3

[0030] Non-Foam Polyurethane Formulation and the Effect of Varying theQuantity of Metal Salt

[0031] A 0.5% solution of copper chloride (10 g) is added to 190 g ofMetacure T-12 and mixed until the copper chloride dissolved. Theresulting copper chloride solution (165 g) was mixed with 8200 grams ofpolyol-234-630 (polyglycol, available from BASF, N.J.), and thissolution is mixed with 1300 grams of trisopropanolamine 99 (availablefrom Dow Chemical USA, MO) at room temperature. This solution (30.4 g)is then vigorously mixed with 455 g of Vibrathane 8011 at 90-110° F. Themixture was then poured into multiple cavity molds and cured at 220-250°F. for 30 minutes. It was demolded and post-cured in an oven at 220 F.for 12 hours. The urethane rubber had a resultant of 3.5×10⁹ ohms-cm.

[0032] The amount of copper chloride in the material was 0.03%. Furthermaterials were made in which the quantity of copper chloride wasincreased while the remaining materials remained the same. Theresistivity dropped (more conductivity) as the level of copper chlorideincreased, as follows: Amount (grams) of CuCl₂ per 100 g of polyolResistivity (ohms-cm) 5.0 × 10⁻⁶  4.0 × 10¹⁰ 5.0 × 10⁻⁵ 3.5 × 10⁹   7 ×10⁻⁵ 3.0 × 10⁹ 9.4 × 10⁻⁵ 2.1 × 10⁹ 1.5 × 10⁻⁴ 1.7 × 10⁹ 2.0 × 10⁻⁴ 1.2× 10⁹ 3.0 × 10⁻⁴ 9.0 × 10⁸ 5.0 × 10⁻⁴ 7.0 × 10⁸ 9.0 × 10⁻³ 2.0 × 10⁸ 1.4× 10⁻² 7.6 × 10⁷ 1.9 × 10⁻² 1.8 × 10⁷ 2.5 4.4 × 10⁶ 5.0 5.0 × 10⁵

EXAMPLE 4 Other Non-Foam Polyurethane Formulations

[0033] A metal salt solution (25%) was formulated with 15 grams of themetal salt; 20 grams of a flame retardant, tri-(B-chloropropyl)phosphate; 20 grams of Isonol 93; and 5 grams of tributoxyethylphosphate. The metal salts that were used in the solution included zincchloride, cobalt chloride, iron oxalate, lithium chloride, copperbromide chromium chloride, and copper chloride, all of which werepurchased from Aldrich Chemical Co. of Milwaukee, Wis. The salts wereground and dried prior to use. The solutions were prepared bymechanically mixing at 200-500 rpm at 150° F. for 1-3 hours.

[0034] The 25% metal salt solution (50 grams) was combined with a 38grams of an extender MOCA (4,4″-diamino-3,3″-dichlorodiphenylmethane,available from Palmer Davis Seikra, Inc., NY), and a polyurethaneprepolymer, Vibrathane B-601 (a polyester/TDI prepolymer, available fromUniroyal Chemical). This was done by adding first the MOCA and then theprepolymer to the metal solution, with mixing, at 180-220° F. Vigorousmixing continued for 2-5 minutes.

[0035] The mixtures were then poured into a multiplecavity metal mold,and the prepolymer was cured at 220-250° F. for 30 minutes. The materialwas removed from the mold and post-cured in an oven for 12 to 20 hoursat 200° F., after which curing was completed by letting the material sitat room temperature for at least 3 days to complete curing.

[0036] The polymeric materials that were obtained had the followingresistivities: Salt Resistivity (ohms-cm) zinc chloride  2.5 × 10¹⁰cobalt chloride  1.2 × 10¹⁰ iron chloride 1.0 × 10⁶ iron oxalate  1.3 ×10¹⁰ lithium chloride  1.6 × 10¹⁰ copper bromide   1 × 10⁶ chromiumchloride  1.9 × 10¹⁰ copper chloride 5.0 × 10⁶

EXAMPLE 5 Polyurethane Foams

[0037] The following conductive foams were prepared according to thesame general procedure used above. The numbers in the table are thegrams of the particular ingredient included in the example. The metalsalt solutions were prepared as described previously; a foam agent suchas methylene chloride, H₂O was used. The notes at the end of the tablesupply further information concerning the ingredients. Example #Ingredients 1 2 3 4 5 6 7 8 P-380¹ 450 325 143 155 180 180 180 400 DC200² 1.8 1.8 6.6 10 7 6.6 7 7 Black #4800³ 6 6 2.33 3.5 5 2.33 5 —Methylene 6 16 4.33 65 4.33 4.33 4.33 4.33 chloride Water 3.5 3.5 1.32.25 1 1 1 0.5 DABCO⁴ 3.5 3.5 1.1 0.5 0.5 1.16 1 1 drop drop B-9-88⁵ 1 10.33 0.5 0.33 0.33 0.33 20 T-12⁶ 0.1 0.1 — — — — — — Mondure PF⁷ 120 12056.7 70 50 50 50 53 (22.6%) Metal Salt — 0.5 33.3 25 40 40 40 60 FormulaCuCl₂ CuCl₂ FeCl₂ FeCl₂ CuCl₂ FeCl₂ CuCl₂ CuCl₂ Solution 25% 25% 25% 25%15% 20% 20% 2% Shore A 15Å 20Å 20Å 20Å 15Å 20Å 10Å 30Å Resistivity 5 ×10¹⁰ 3 × 10⁹ 1.2 × 10⁸ 9 × 10⁷ 5 × 10⁷ 3.8 × 10⁷ 3 × 10⁷ 8 × 10⁶(OHMS-cm)

[0038] 1. P-380 (Pluracol polyol 380) is a polyether polyol availablefrom BASF Corporation of Wyandotte, Mo.

[0039] 2. A silicone surfactant available from Dow Corning.

[0040] 3. Black #4800 is a black pigment from Pigment Dispersions, Inc.

[0041] 4. DABCO is a triethylenediamine catalyst available from AirProducts, Inc.

[0042] 5. B-9-88 (Benzoflex 9-88) is a benzoate ester plasticizeravailable from Harcros Chemicals Inc.

[0043] 6. T-12 is Metacure T-12 catalyst.

[0044] A further example of a conductive polyurethane foam included 60 gof 20% copper chloride solution, prepared as previously described; 3.5 gof trimethylolpropane, (available from Celanese Chemical Company ofDallas, Tex.); 7 g of DC 200; 0.5 g of water; 4.3 g of methylenechloride; 20 g of the B-9-88; and 400 g of Vibrathane 8011. The materialwas prepared by following the same general procedures previouslydescribed. The foam had a resistivity of 8×10⁶ ohm/cm.

EXAMPLE 6 Semiconductive Rubber

[0045] Conductive rubber materials are prepared as follows.

[0046] Iron Chloride (15 g, purchased from Johnson Mathley Electronicsof Ward Hill, Mass.) are added to 85 g of the plasticizer dibutylphthalate. The mixture is heated to 200° C. and mechanically stirred for4 hours. A dark solution is obtained.

[0047] This solution is mixed with rubber materials (such as naturalrubber, nitrile rubber, EPDM, styrene butadiene rubber, neoprene rubber,polysulfide rubber), and polyacrylate rubber, sulfer, and additives forrubber compounding. The rubber was then compression molded at 300psi and300° F. for 20 minutes to cure the rubber.

EXAMPLE 7 Adhesive

[0048] A copper chloride solution is mixed with a curative and adhesive,such as Thixon 405 (available from Morton International), Chemlok 205,213, and 214 (available from Lord Corp.), and Conap 1146 (available fromConap Corp). These adhesives were mixed with copper chloride solutionsto provide rubber materials with resistivities of between 1×10⁷ ohms-cmand 1×10¹² ohms-cm. It is then coated on metal surfaces, dried andcasted with urethane rubber.

EXAMPLE 8 Hot Melt

[0049] Plastic materials are melted and mixed with metal salts underheat. The molten polymer was poured with into mold to form conductiveparts, “cure”, as used herein, is meant to include this procedure, aswell as procedures in which the prepolymer actually cross-links andchemically reacts to form further bonds. The plastic material usedshould contain electrons donor groups or atoms such as oxygen, nitrogen,sulfur, halides, or unsaturated bonds. The plastic material can be, forexample, a polycarbonate, polyimide, polyamide, polysulfer, orfluorocarbon.

[0050] Other embodiments are within the following claims.

1. An electrically conductive or semi-conductive polymeric material,comprising a solid solution of metal salt in polymer, said metal saltbeing completed with said polymer to provide said material with aresistivity of between about 10¹² ohms-cm and 10⁵ ohms-cm.
 2. Thepolymeric material of claim 1, wherein said polymeric material comprisesless than 5% of said metal salt by weight.
 3. The polymeric material ofclaim 2, wherein said polymeric material comprises less than 0.2% ofsaid metal salt by weight.
 4. The polymeric material of claim 1, whereinthe molecular size of said metal salt is of between about 1Å and 10 Å.5. The polymeric material of claim 1, wherein said polymer is anelastomeric polymer.
 6. The polymeric material of claim 1, wherein saidpolymer is a polyurethane foam.
 7. The polymeric material of claim 5,wherein said elastomeric polymer is a polyurethane.
 8. The polymericmaterial of claim 5, wherein said elastomeric polymer is a rubber. 9.The polymeric material of claim 8, wherein said rubber is selected fromthe group consisting of nitriles, natural rubbers, neoprenes,fluorocarbons, and silicones.
 10. The polymeric material of claim 8,said material further comprising a plasticizer.
 11. The polymericmaterial of claim 1, wherein said polymeric material comprises less than1% of said metal salt by weight.
 12. The polymeric material of claim 1,wherein said polymer is an adhesive polymer.
 13. The polymeric materialof claim 1, wherein said polymer is a plastic, containing electrondonating substituents.
 14. The polymeric material of claim 1, whereinsaid material has a resistivity of between about 10⁷ ohms-cm and 10⁹ohms-cm.
 15. The polymeric material of claim 1, wherein said metal saltis a transition metal halide.
 16. The polymeric material of claim 1,wherein said metal salt is selected from the group consisting of CuCl₂,CuBr₂, CoCl₂, ZnCl₂, NiCl₂, FeCl₂, Cu(NO₃)₂, FeBr₂, LiBF₄, andH₄Fe(CN)₆, CuI₂, FeI₃, FeCl³, FeBr₃, copper lactate, copper tartrateiron phosphate, and iron oxalate.
 17. A roller comprising a cylinderhaving a surface comprising a conductive or semi-conductive polymericmaterial comprising a solid solution of a metal salt in a polymer,wherein said metal salt is complexed with said polymer to provide saidpolymeric material with a resistivity of between about 10¹² ohms-cm and10 ⁵ ohms-cm.
 18. The roller of claim 17 wherein said polymeric materialcomprises a polyurethane polymer.
 19. A method of making an electricallyconductive or semi-conductive polymeric material having a resistivity ofbetween 10¹² ohms-cm and 10⁵ ohms-cm, said method comprising mixing ametal salt with a polymer or polymer precursor to provide a solutionthat includes said metal salt and said polymer or polymer precursor;curing said solution to provide a polymeric material in which said metalsalt is complexed to said polymer or a polymer produced from saidpolymer precursor; wherein a sufficient quantity of said metal salt ismixed with said polymer of polymer precursor so that the resistivity ofsaid polymeric material is between 10¹⁰ ohms-cm and 10⁵ ohms-cm.
 20. Themethod of claim 19 wherein said polymeric material comprises less than1% of said metal salt by weight.
 21. The method of claim 19, whereinsaid polymer precursor is an isocyanate-functional prepolymer.
 22. Themethod of claim 19, wherein an extender is also mixed with said polymerprecursor and said metal salt to provide said curable mixture.
 23. Themethod of claim 19, wherein said extender is a polyol or a polyamine.